I need so much help

Sundar used linear combination to solve the system of equations shown. he did so by multiplying the first equation by 5 and the second equation by another number to eliminate the y-terms. what number did sundar multiply the second equation by? 2x+9y=41 3x+5y=36

Susie wants to take her friend out for lunch.she wants to spend $9.75 each person. how much will she spend in all.

Idon't get undoing if its pass adding and subtracting so can someone ? x-2 over 5 = 18